This invention relates to vertical and/or short takeoff and landing (V/STOL) airplanes and in particular to improved method, system, and apparatus for vectoring the aircraft engine exhaust flow with a system of trailing edge flaps to achieve vertical and/or short takeoffs and landings.
Several types of so called V/STOL aircraft have been proposed. One type, exemplified in U.S. Pat. No. 3,096,954, Bauger et al, uses an articulated cylindrical duct through which a turbofan exhaust is discharged. This type of system has relatively low efficiency due to large losses in turning the exhaust. One loss occurs in the fan exhaust duct on the outside of the turn, where the turning of the exhaust by the nozzle duct wall tends to generate contrarotating vortices. These vortices form a blockage in the duct, causing a thrust loss. Also mixing of the fan exhaust with the hot core or turbine exhaust limits the augmentation ratio available because of a requirement to match the pressures of the two streams.
Another proposal is shown in U.S. Pat. No. 3,330,500 to Winborn. In this propulsive wing type, the fan discharge is vectored through lower surface flaps at approximately the mid cord of the propulsive wing, while the hot turbine exhaust is discharged at the upper trailing edge of the propulsive wing. The discharge of a high energy jet at mid chord on the lower surface of the wing will cause high suckdown forces on the wing and may even be large enough to prevent lift-off.
Another disadvantage of designs such as the Winborn patent referred to above is in the arrangement of the deflecting flaps for the fan exhaust. Several flaps are spaced across the fan nozzle, forming a cascade and vertically dividing the exhaust stream into several layers. The flaps all pivot downwardly, turning the individual layers of air. The several flaps in the mainstream create drag, causing a loss in thrust efficiency. Another disadvantage is that due to their positioning, the total nozzle area varies as the flaps move from the horizontal to downward positions. The variance can detrimentally affect the thrust during transition positions. Another example of this cascade flap arrangement is shown in U.S. Pat. No. 4,000,868, Gregor.
One manner in which certain types of airplanes have improved the lift at low speeds is by bleeding a portion of the jet engine exhaust air or fan air over the upper surface of a wing trailing edge flap. An example of this system is shown in U.S. Pat. No. 3,920,203 to Moorehead. The high energy sheet of air being discharged delays or prevents boundary layer air flow separation. Boundary layer separation as used in this context refers to the separation of an airstream flowing over an airfoil from the airfoil surface. At and after the point of separation, a higher static pressure turbulent area exists between the airstream and airfoil, causing drag and reducing the lifting potential. The high energy sheet of air being ejected over the flap retards or prevents this separation. Also, the jet sheet can induce, by jet pumping action, additional flow over a wing to increase its circulation or lift, this increased circulation being known as super circulation.
Bleeding a portion of the exhaust over a trailing edge flap has been used, with the energy level of the jet sheet at moderate levels, to successfully improve the low speed characteristics of conventional takeoff and landing airplanes, as shown in the Moorehead patent.
One proposal, shown in U.S. Pat. No. 2,879,957, Lippisch, proposes to utilize the propulsion system to create super circulation in a V/STOL airplane. One deficiency in the design disclosed therein is that it is unlikely that the sheet of air could exit through the upper slot since higher pressure air exists on the upper surface of the nacelle. Means would have to be provided to scoop the airflow out. The Lippisch design also utilizes the high drag cascade system of flaps, and has other disadvantages as well.